1.1. Field of the Invention
This invention relates to electric field dependent/responsive fluids such as the so-called "electrorheological" or "electroviscous" fluids. More specifically, the invention relates to the use of improved electric field dependent fluids wherein the fluids exhibit a reversible rise in viscosity and a corresponding change in dynamic torque transmission in the presence of high voltage at temperatures in excess of 100.degree. C. without the deleterious release of water.
2.2. Description of the Prior Art
It is generally known that electroviscous or electrorheological fluids exhibit pronounced changes in viscosity and resistance to shear in response to the application of an electric field. Such fluids generally comprise suspensions of finely divided, solid particles which intentionally contain a certain amount of adsorbed water dispersed in a nonconductive, hydrophobic liquid. The presence of the water has been acknowledged as being a critical and mechanistically necessary element in achieving the desired change in viscosity under the influence of an applied electric field. Thus for example, U.S. Pat. No. 3,047,507 teaches and claims the addition of excess or adsorbed water as do U.S. Pat. No. 4,483,788; 4,033,892; and 4,129,513. In explaining mechanistically the role of adsorbed water it is postulated that the presence of adsorbed water in or on the particulate material is necessary to promote ionization and thus allow charges to move freely on the surface of the particles when an electric field is imposed. However, because of the intentional presence of adsorbed water in the electroviscous fluids of the prior art, such compositions are restricted to low temperature end use applications. In high temperature applications or in high shear rate applications wherein a shear induced exotherm can occur, free water or water vapor will be produced, thus representing a potentially corrosive environment, which severely limits these prior art electroviscous fluid systems.
In a recent British patent application No. 2,170,510, an electrorheological fluid comprising a liquid continuous phase and a dispersed, substantially anhydrous phase is disclosed. Acceptable dispersed particulate phase includes semiconductor, unsaturated fused polycyclic compounds and poly(acene-quinone) polymers. However, this reference deals exclusively with electrorheological properties at static flow conditions and does not disclose the improved compositions of the present invention.